As it is well-known (see Perry's Chemical Engineer's Handbook, 6.sup.th edition, 9-40 Energy utilization, convension and resource conservation FIGS. 9-32 Basic types of mechanical stockers), removal of carbon deposits on solid objects by oxidation and/or gasification can be carried out in the same way as a coal combustion operation, on a travelling grate as shown in FIG. 1. The feed to be treated 1, stored in an enclosure, is laid gravitationally on a travelling grate 2 mounted on two rotating cylinders 3. The layer 4 formed is generally a few centimeters thick. It is heated by a heating means 5 mounted on a radiant arch 6, which may be a burner using an auxiliary fuel such as fuel oil or natural gas. The air or the gasification agent is injected below grate 2, it flows through layer 4, thanks to one or more vessels 7. The gas flow rates in each vessel can be adjusted individually in order to best adjust the thermal profile of the layer and to optimize conversion of the feed. The treated solids are discharged through device 8, whereas the gaseous effluents resulting from the treatment are extracted through a specific line and most often sent to a boiler or a heat exchanger for energy recovery.
This well-known type of device only allows to treat objects of a given size (characteristic size larger than 1 cm) because of channeling problems through the travelling grate and dust falls.
The treating temperatures are difficult to control because of the fixed nature of the layer formed, a layer in which thermal exchanges are low by definition.
Finally, travelling grate 2 regularly poses mechanical, fouling, sticking problems, etc.
Some of these drawbacks can be eliminated by using fluidized bed systems as shown in FIG. 2. According to this known concept, the feed to be treated, stored in an enclosure 11, is fed gravitationally into fluidized bed 12. The fluidized medium is obtained by blowing air or a gasification agent through a diffuser 13 under conditions known to the man skilled in the art. The treated solids are discharged, for example by overflow through a line 14, while the gaseous effluents leave the device via a pipe 15 and are sent for example to an exchanger on a recovery boiler.
This device must necessarily be equipped with a preheating means 16, that can be for example a combustion chamber for an auxiliary fuel placed on the air or gasification agent circuit.
In the case where the amount of heat produced in the fluidized medium is large, calories can be extracted by means of an immersed exchanger 17 in order to maintain the temperature of the medium within a given range.
This type of device (fluidized bed) allows to treat small-size objects (from several ten microns to a few millimeters) under precise temperature control conditions. However, it has several drawbacks; first, it performs like a perfectly agitated reactor, so that some of the solid objects leave the system shortly after they entered it. They are therefore not properly treated.
Furthermore, the fluidized medium is very erosive because of the friction of the objects against each other, especially in the vicinity of the air inlets. Using such a system should therefore be avoided when treating objects whose mechanical strength is limited.
These attrition problems can also lead to the presence of significant amounts of dust in the gaseous effluents, a dust that has to be removed before said gaseous effluents are discharged into the atmosphere.
Besides, the pressure drops in the gas circuit are higher than in the system using a travelling grate and they can be disadvantageous in some cases. Finally, the fluidized bed technology is generally rather complex from the mechanical point of view, and therefore expensive.
Besides, French patent application FR-2,634,187 discloses a vibrating bed system with a closed trough of substantially concave section.
Furthermore, French patent application FR-2,702,392 filed in the name of the applicant discloses a vibrating-elevator device for regeneration of absorbents used in fumes desulfurization. However, this device does not allow proper treatment of the "sticky" products of very small grain size (&lt;20 microns). This document describes various means for heating and cooling the device, with either a burner or an exchange trough.
French patent application EN.97/02,658 filed in the name of the applicant discloses a vibrating elevator reactor consisting of a substantially cylindrical helical tube, intended for regeneration of reforming catalysts.
None of the aforementioned known devices allows to remove carbon deposits on solids with sizes greater than or equal to one centimeter.